Wood Column Capacity (Slenderness)
Slenderness ratio, column stability factor Cp, allowable Fc-prime.
Example
You enter
- Column width b (in) 3.5
- Column depth d (in) 3.5
- Unbraced length lu (in) - Ke is applied below 96
- Fc* (psi) 1150
- Emin (psi) 580000
- Effective-length factor Ke 1
You get
- Allowable axial capacity 6600 lb
- Column stability factor Cp 0.4685
Details, formula, and sources
Slenderness ratio, column stability factor Cp, allowable Fc-prime, and allowable axial capacity for a solid rectangular sawn-lumber column via the NDS Cp / Euler buckling basis.
le/d governs (smaller dimension); FcE = 0.822*Emin/(le/d)^2; a = FcE/Fc*; c = 0.8 (sawn); Cp = (1+a)/(2c) - sqrt(((1+a)/(2c))^2 - a/c); Fc' = Fc**Cp; capacity = Fc'*b*d.
Per the NDS column-stability provisions (the Cp / Euler buckling basis), by name; reference design values user-supplied.
AWC publishes the NDS free read-only at awc.org; the IBC-adopted edition governs.
Estimate. AHJ and licensed professional govern.
Field names used by the API: b_in, d_in, le_in, fc_star_psi, emin_psi, ke, capacity_lb, cp
- c factor 0.8 for sawn lumber (0.85 round poles, 0.9 glulam)NDS section 3.7